Search

Estrogen deficiency-induced postmenopausal osteoporosis has become a worldwide problem, inducing low bone mass and microarchitectural deterioration of the bone scaffolding in the vertebrae and long bones. With the prevalence of such osteoporosis on the increase, the influence of this estrogen deficiency on the jaw bones has drawn the attention of researchers and clinicians in the field of dentistry. The aim of this article is therefore to review the microstructural changes occurring after ovariectomy in the jaw bones of animal subjects. Induced estrogen deficiency clearly led to structural changes in the jaw bones and alveolar bone of animal subjects (rats and monkeys). Severe bone loss in the rat alveolar bone was principally caused by high bone resorptive activity. This activity accelerated greatly immediately after ovariectomy, and was then followed by more moderate resorptive activity, which continued over an extended period. Additionally, occlusal hypofunction further greatly accelerated the fragility of the alveolar bone structure in ovariectomized rats. Microstructural damage also seen in the alveolar bone of ovariectomized monkeys was found to be directly connected to their systemic osteoporosis. Recent investigations of the relationship in humans between systemic osteoporosis and jaw bone loss have also suggested that a connection may exist between these two. However, more research is required to confirm this connection in humans as well.

In order to prove osteocytic osteolysis in vivo, human parathyroid hormone (hPTH (1-34), 749 ng/h), or only solvent of the same volume, was continuously administered to 8-month-old rats by an infusion pump for 4 weeks, and then structural changes in osteocytes in the cortical bones of the tibiae were analyzed morphometrically, histologically, and histochemically. Based on contact microradiography (CMR) observations, the osteocyte lacunae in the PTH group tended to be enlarged, compared with those of the control, while the average lacuna area was 137.0 microm2 in the PTH group versus 93.9 microm2 in the control, suggesting evidence of osteocytic osteolysis. Acid phosphatase enzyme histochemical localization was observed in some osteocytes in the PTH group; therefore, lysosome systems may participate in the osteolytic mechanisms. On histological samples stained with hematoxylin-eosin or toluidine blue, the lacunae of the controls were surrounded by narrow areas of matrices both positive for hematoxylin and metachromatic for toluidine blue, while belt-like areas positive for hematoxylin were observed around the PTH-group lacunae. These findings suggested that, after osteocytic osteolysis, regenerated bone matrices may be added to the walls of osteocytes that possess enlarged lacunae.